The present invention relates to improvements in a copier having a sorter, by which images can be transferred onto both sides of a recording paper.
In general, this kind of copier comprises: a document feeder which feeds an uppermost or lowermost document stacked on a document tray onto a platen glass and returns the document to the tray after predetermined processing so as to be fed again; and an intermediate tray on which recording papers are stacked. The document image is recorded on one side of the recording paper, and when the lowermost recording paper on the intermediate tray is fed to a transfer section, it is reversed, so that images on one side of the document can be recorded onto one side or both sides of the recording paper. In this copier, when a document feeder in which a document can be reversed is utilized, document images on both sides can be recorded on one side or both sides of a recording paper.
After the aforementioned image forming operation, the recording paper is sorted by a sorter provided to one side of the copier.
In a two-sided copying operation by the aforementioned conventional copier, two kinds of processing modes are known, which are determined according to document conveyance procedure and recording paper reversal procedure.
The form and time characteristics of the aforementioned two modes will be explained as follows.
For simplification, explanation will be made under the conditions that a document image is provided only on one side, and that the following are already known: the number of documents (the number of pages) is 2M; and the number of sets of copied papers is N.
There is a difference in the conveyance procedure of a document and that of a recording paper depending whether the number of documents is odd or even. However, this difference is not essential to the present invention, so the following explanation will be made under the condition that the number is even.